Such electric toothbrushes have widely been put to practical use as one which linearly reciprocates a cleaning head having a plurality of bristle bundles implanted therein in a direction generally perpendicular to an implanted direction of the bristle bundles, one which inversionally reciprocate the cleaning head around the implanted direction of the bristle bundles, one which vibrates the cleaning head together with a casing, and the like. In this regard, the inversional reciprocation in this specification indicates a movement which repeatedly carries out such a rotational movement that the cleaning head rotates a certain degree of angle in a forward direction and then rotates the same degree of angle in a reverse direction.
Further, as driving means of the electric toothbrush which linearly reciprocates the cleaning head, driving means which is provided with a converting means such as a crank mechanism for converting a rotational movement of a rotational shaft of a motor to a linear reciprocation of an output shaft is widely employed because of its low manufacturing cost. However, since a vibrational frequency of the cleaning head is limited when it is linearly reciprocated by a motor, an electric toothbrush which uses a linear actuator having a permanent magnet and a coil has also been put to practical use recently in order to improve a cleaning efficiency by increasing the vibrational frequency of the cleaning head.
As for the electric toothbrush using the linear actuator, there has been proposed one which is provided with a plunger supported so as to reciprocate freely in an axis direction thereof, a spring member which uses a moving part including the plunger as a vibration system, electromagnetic driving means for driving the moving part so as to reciprocate at its resonance frequency when an alternating current is applied thereto, and restricting means for restricting a rotation of the moving part around an axis thereof (see Patent Document 1, for example).
Further, there has also been proposed an electric toothbrush which is provided with a shaft supported so as to linearly reciprocate freely in an axis direction thereof and tubular permanent magnets each having a central axis generally coincident with a central axis of the shaft and both end surface portions each having opposite polarity so that a moving member is constituted by the shaft and the permanent magnets, wherein the moving member is inserted into a tubular stator provided with a winding so as to linearly reciprocate freely and the moving member is reciprocated by applying current to the winding (See Patent Document 2, for example).    Patent Document 1: Japanese Patent Laid-Open Publication No. 2002-176758    Patent Document 2: Japanese Patent Laid-Open Publication No. 2004-343931